Unmanned aircraft (UAV) according to the prior art are increasingly also used for civilian terrain capture and ground observation, in addition to military fields of use. In this case, a predetermined flight route is followed according to a flight plan, wherein a plurality of aerial images and data are captured mostly with a determined image capture frequency and a determined image overlap (adjacent images) along the route by means of a camera or an imaging sensor. Respective triggering points for the image capture are typically defined in the flight plan for this purpose.
In addition, position and alignment data for the aircraft are measured and linked to the respective captured images. The image triggering is triggered, for example, based on captured GPS position data or time data.
The entirety of the data captured during the flight are then processed in the scope of subsequent “post-processing” such that by way of suitable linkage of the images and calculation of the location data, a planar, stereophotogrammetric depiction of the captured terrain and, therefrom, an orthogonal product are created.
In particular light UAVs are very susceptible to wind and are unstable in this case, i.e., the respective location thereof can already be significantly influenced by a few strong gusts of wind or other external influences and changed in an indeterminate manner. The aerial images are thus not each captured with identical alignment or viewing angle of the aircraft, but rather each have an offset not only in the flight direction but rather also, for example, in a direction orthogonal to the flight direction (viewing direction).
Conventional UAVs do not actively consider or correct the spatial location of the system during the data recording and during the triggering of the image recording such that a uniform viewing direction could be guaranteed for the image capture thereby. This negatively impairs the accuracy of the post-processed data, up to resulting data gaps, for example, regions of the area to be surveyed which were not captured in images. Due to the images captured in this case having different viewing directions, the accuracy of the stereo image which can be created therefrom is reduced, for example, as a result of perspective distortions and reduced capability of generating linkage points between the individual images. These are necessary for accurate alignment of the stereo images and registration of the data with one another in the case of inaccurate GPS determination.
If the UAV is engaged by a gust of wind and thus strongly inclined, for example, in relation to a nadir alignment or horizontal alignment of the UAV, the desired terrain region thus cannot be captured in the case of an aerial image capture occurring at this time, but rather, depending on the deflection of the UAV, an adjacent region or even a region which has no overlap with previously captured images.
Such a data gap is usually closed by repeated overflights and further image capture of the relevant region, wherein this is relatively time-consuming.